Molten plastic is fed to molds for the formation of plastic molded parts. Shut-off valves to control the flow of the plastic to the mold have been provided which are of generally cylindrical shape and have an axial plastic flow path therethrough. The downstream end of the valve has an orifice which is open for plastic flow when required and is closed by an axially reciprocal closure element. The interior arrangement of the parts in such prior art valves is deficient in that uneven heating of metal surrounding the reciprocal closure element occurs, leading to possible seizure of the unit and inefficient closure may occur due to misalignment of the closure element and the orifice.